Project Summary Rather than being considered as another phase of the lifespan, aging is now considered a major risk factor for heart diseases. One of these age-triggered diseases is the dysfunction of the natural pacemaker of the heart, the sinoatrial node (SAN). SAN dysfunction is the cause of 50% of the over 200.000 artificial pacemakers implanted every year in the US. SAN pacemaking function depends on the calcium signaling sustained by voltage-gated ion channels and the internal calcium stores. The long-term of my scientific career is to understand how aging remodels calcium signaling in the heart and how this relates with the onset of heart diseases. This K99/R00 proposal is the starting point, where I will determine how aging changes the expression and distribution of voltage gated L-type calcium channels. Despite that L-type calcium channels are the channels that sustain the action potential in SAN cells, the changes that these channels undergo during aging are poorly explored. This proposal is divided in two phases: the training K99 phase will focus on the study of the coupling of L-type calcium channels, its role in the pacemaking and how it is affected by aging. This channel coupling is a new mechanism of calcium facilitation that I discovered in hippocampal neurons and that have not been studied in the SAN. During the training phase I will also build technical and academic skills on aging and cardiac physiology. The independent R00 phase will focus on how aging changes the expression, distribution and function of L-type calcium channels. For this part I will take advantage of my previous training and expertise on the study of CaV1.3 channels. I will use electrophysiology to characterize the biophysical properties of the L-type calcium channels in young and old mice. I will use mutant mice strains (CaV1.3-/- and CaV1.2DHPins) to dissect the components of the L-type calcium current and find if aging regulates them differentially. In addition, I will use expansion microscopy and super-resolution imaging to generate maps of the change in the expression and distribution of CaV1.2 and CaV1.3 channels in the SAN during aging. This tool will be useful for further studies in the remodeling of protein in the SAN during aging. Together these results will serve as the foundation of my first R01 and will launch the beginning of my independent research career. For a successful transition to the independence I will count with the mentoring of a team of experts in cardiac and aging physiology, including Dr. Fernando Santana, Dr. Edward Lakatta, Dr. Nipavan Chiamvimonvat and Dr. Donald Bers. They will follow very close my experimental and academic training and help me to establish my career development strategies. The diverse array of expertise and the highly interactive scientific environment at UC Davis is particularly well-suited to foster and support this proposal. The K99/R00 award constitutes a unique opportunity for my advance in the academic track. It will help me to consolidate an innovative niche on the study of the aging of calcium signaling and provide me with the necessary academic and technical training to launch my career as an independent investigator.